[RichD]

What is the physics/acoustics of a wind instrument?

It's easy to see how a percussive surface vibrates, and
induces acoustic waves at the same frequency.
Ditto a string.

But pushing air through a trumpet (sax, etc.), then out
the bell - how does that create sound? And in particular,
how does the valve action produce controllable wave
sequences (a/k/a music)? It's just air on air, I'm at a
loss to explain it.

--
Rich

[M J Carley]

In the referenced article, RichD writes:

What is the physics/acoustics of a wind instrument?

The best place to look is probably Neville Fletcher's work:

http://www.phys.unsw.edu.au/jw/brassacoustics.html
--
Qualcuno era comunista perché abbiamo il peggiore Partito Socialista d'Europa.
Qualcuno era comunista perché lo Stato peggio che da noi solo l'Uganda.

Michael Carley: http://people.bath.ac.uk/ensmjc/

[Sam Wormley]

On 12/9/10 11:19 AM, RichD wrote:
What is the physics/acoustics of a wind instrument

http://hyperphysics.phy-astr.gsu.edu...es/clocol.html
http://hyperphysics.phy-astr.gsu.edu...opecol.html#c2
http://hyperphysics.phy-astr.gsu.edu...locol2.html#c1

[Angelo Campanella]

"Sam Wormley" wrote in message
...
On 12/9/10 11:19 AM, RichD wrote:
What is the physics/acoustics of a wind instrument
http://hyperphysics.phy-astr.gsu.edu...es/clocol.html
This assumes a closed end, promoting only odd harmonics,

http://hyperphysics.phy-astr.gsu.edu...opecol.html#c2
This discusses closed and open ends, promoting odd-only as well as both odd
and even harmonics.

http://hyperphysics.phy-astr.gsu.edu...locol2.html#c1
This discusses the conical column as well, and I'm not sure I go along with
his rationales as to why it behaves differently.
I am told that clarinets and other tapered-bore wind instruments, do not
emit even harmonics in their timbre. This implies that those instruments
have the characteristics of a closed-end tube. My thought is that the
conical bore acts as a barrier or reflector for a sound wave reflecting from
the opening back into the bore because that closing bore impedes propagation
back up said bore toward the tiny mouthpiece opening..

Ange.

[RichD]

Forgot about this one -

On Dec 9, "Angelo Campanella" wrote:
What is the physics/acoustics of a wind instrument
http://hyperphysics.phy-astr.gsu.edu...es/clocol.html

This assumes a closed end, promoting only odd harmonics,

http://hyperphysics.phy-astr.gsu.edu...opecol.html#c2

This discusses closed and open ends, promoting odd-only
as well as both odd and even harmonics.

This is what I don't get.
How do you get a reflection from the open end?
I can't picture that. It doesn't jibe with my (fading)
memory of studying transmission lines, in EM,
where you get standing waves, with a termination
at each end.

--
Rich

[Scott Dorsey]

RichD wrote:

This is what I don't get.
How do you get a reflection from the open end?
I can't picture that. It doesn't jibe with my (fading)
memory of studying transmission lines, in EM,
where you get standing waves, with a termination
at each end.

No, you DON'T get standing waves with a termination at each end.

If you short the end of the cable, you get an inverted reflection back.
If you leave the end of the cable open, you get a non-inverted reflection
back.

ONLY if the cable is terminated into an impedance equal to the characteristic
impedance of the line do you not get a reflection; the termination load
appears like additional cable and the signal goes quietly into it as if it
were so.

The same thing happens with an open or closed organ pipe and creates the
internal resonance of the pipe.

In a trumpet it gets interesting.... because the bell of a trumpet is
effectively an impedance-matching transformer....
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."